Reprogrammable shape memory ion gels via physical entanglement of ultrahigh molecular weight polymers

Abstract

In this study, we develop shape memory ion gels comprising ultrahigh molecular weight (UHMW) polymers and ionic liquids (ILs), synthesised via a facile one-pot radical polymerisation method of vinyl monomers in the IL medium. The resulting ion gels exhibit a high glass transition temperature (T_g) above room temperature and a broad rubbery plateau, attributed to the abundant physical entanglements of the UHMW polymers in the IL medium. Dynamic mechanical analysis confirms their excellent shape-memory performance, including triple shape-memory behaviour. By leveraging the nonvolatility of IL, the ion gels can be recycled through thermal remoulding with minimal degradation in their mechanical properties. Furthermore, they retain their shape-memory performance over multiple deformation cycles with negligible residual strain, in contrast to their counterparts containing lower molecular weight polymers, which suffer from chain pullout and incomplete recovery. Notably, this study demonstrates that densely entangled polymer networks can enable shape reprogramming, highlighting physical entanglements as a robust and dynamic cross-linking motif. Moreover, the T_g can be finely tuned by adjusting the polymer/IL composition or by selecting different IL structures, offering a versatile strategy for designing high-performance shape memory materials.